Composition, apparatus, and method of conditioning scale on a metal surface

Abstract

A composition and apparatus and method of using the composition for aqueous spray descaling or conditioning of scale or oxide on metal surfaces, especially stainless steel strip or the like, in one embodiment, although it can be used to descale or condition oxide or scale on other work pieces such as metal bar, or even discrete objects. An aqueous solution having a base composition of an alkali metal hydroxide, such as sodium hydroxide, potassium hydroxide, or a mixture of alkali metal hydroxides such as sodium hydroxide and potassium hydroxide is used. The aqueous solution may contain certain additives to improve the descaling performance of the salt. In one embodiment, the solution is used to condition the scale or surface oxide on a strip of stainless steel. The strip of steel is at a temperature between the melting point of the alkali metal hydroxide in anhydrous form and a temperature at which the Leidenfrost effect appears. One or more nozzles is provided to spray the solution, and the heated strip is passed by the nozzle or nozzles where the solution is sprayed on the surface or surfaces of the strip that have the scale or oxide. The invention also includes the apparatus and control thereof for the spraying of the solution.

What is claimed is:  
     
       1. A method of treating scale on the surface of a metal object comprising the steps of: 
       a) providing a metal object with scale thereon;  
       b) providing an aqueous solution comprised of an alkali metal hydroxide or mixture of alkali metal hydroxides;  
       c) controlling the temperature of the surface of the metal object to a temperature above the melting point of the alkali metal hydroxide or hydroxides in anhydrous form and where conditioning occurs, and below the temperature at which the Leidenfrost effect appears; and  
       d) thereafter spraying said solution on the surface of the metal object.  
     
     
       2. The method as defined in  claim 1  wherein the solution contains sodium hydroxide or potassium hydroxide or a mixture thereof. 
     
     
       3. The method as defined in  claim 1  wherein the metal object is acid pickled after spraying with said solution. 
     
     
       4. The method of  claim 1  wherein the concentration of the solution is between about 15% and 65% solids by weight. 
     
     
       5. The method as defined in  claim 1  wherein the solution concentration is between about 35% and 45% solids by weight. 
     
     
       6. The method as defined is  claim 1  wherein the concentration of the solution is about 40% solids by weight. 
     
     
       7. The method as defined in  claim 1  wherein the temperature of the surface of the metal object is at least about 450° F., and does not exceed about 700° F., as measured by a contact thermocouple. 
     
     
       8. The method as defined in  claim 4  wherein the temperature of the surface of the metal object is at least about 450° F. and does not exceed about 600° F., as measured by a contact thermocouple. 
     
     
       9. The method as defined in  claim 1  wherein the metal object is stainless steel strip. 
     
     
       10. The method of  claim 1  wherein the solution contains an effective amount of an additive selected from the group of alkali metal carbonates, alkali metal chlorates, alkali metal nitrates, alkali metal permanganates, and mixtures thereof. 
     
     
       11. The method of  claim 10  wherein the additive is an alkali metal permanganate. 
     
     
       12. The method of  claim 2  wherein aqueous solution is comprised of a eutectic mixture of sodium hydroxide and potassium hydroxide. 
     
     
       13. The method of  claim 1 , further comprising the steps of: 
       a) providing a composition and dimensions for the metal object; and  
       b) controlling the amount of the solution sprayed on the surface of the metal object;  
       wherein the step of controlling the amount of the solution sprayed is responsive to at least one of the composition and the dimensions of the metal object. 
     
     
       14. The method of  claim 13 , further comprising the step of analyzing the sprayed metal object surface to measure the degree of surface scale conditioning; and wherein the step of controlling the amount of the solution sprayed is further responsive to the step of analyzing said sprayed metal object surface. 
     
     
       15. The method of  claim 1  wherein the step of spraying said solution on the surface of the metal object is performed in an oxidizing atmosphere.